Frequency offset compensating apparatus and method, and optical coherent receiver

Abstract

The present invention relates to a frequency offset compensating apparatus and method, and an optical coherent receiver. The optical coherent receiver includes a front end processor and a frequency offset estimator, of which said front end processor converts an inputted optical signal into a base band digital electric signal, and said frequency offset estimator estimates a phase offset change introduced by a frequency offset in said base band digital electric signal; said frequency offset compensating apparatus comprises an M output integrator, for integrating the phase offset change introduced by the frequency offset to acquire M inverse numbers of the phase offset introduced by the frequency offset, where M is an integer greater than 1; a series-parallel converting device, for dividing said base band digital electric signal into M sub base band digital electric signals; M complex multipliers, for constructing the corresponding inverse numbers in the M inverse numbers to be complex numbers, and multiplying them with the corresponding sub base band digital electric signals in the M sub base band digital electric signals; and a parallel-series converting device, for converting the M sub base band digital electric signals multiplied by said complex multipliers into a base band electric signal.

Description

FIELD OF THE INVENTION[0001]The present invention relates to optical communications, and more particularly, to an optical coherent receiver.BACKGROUND OF THE RELATED ARTS[0002]With the gradual enhancement on the requirements of capacity and flexibility of the optical communication system, the coherent optical communication technology has become more and more important. In comparison with incoherent technology (such as on-off key, OOK) or self-coherent technology (such as differential quadrature phase-shift keying, DQPSK), the coherent technology has the following advantages: optical signal-to-noise ratio (OSNR) gain of approximately 3 dB; the capability to use more efficient modulation technologies (such as quadrature modulation, QAM) to enhance transmission capacity, and the capabilities to make convenient use of electric equalization technology in response to channel change, and lower production cost, etc. Coherent reception requires that the frequency and phase of the local oscil...

AI Technical Summary

Benefits of technology

[0020]Detailed explanations to the present invention with reference to the accompanying drawings make it possible to comprehend the aforementioned and other characteristics, advantages and objectives of the present invention in a clearer manner, in the drawings:

[0021]FIG. 1 shows a known optical coherent receiver employing a phase locked loop;

[0022]FIG. 2 show a prior art optical coherent receiver employing the digital phase recovery technology;

[0023]FIG. 3 shows a frequency offset compensating apparatus according to one embodiment of the present invention;

[0024]FIG. 4 provides two implementation methods of the multi-output integrator shown in FIG. 3B;

[0025]FIG. 5 shows a frequency offset compensating apparatus according to another embodiment of the present invention and a digital phase recovering device incorporating the frequency offset compensating apparatus;

[0026]FIG. 6 shows an optical coherent receiver employing the frequency offset compensating apparatus according to the present invention;

[0027]FIG. 7 shows an optical coherent receiver employing the digital phase recovering device that incorporates frequency offset compensation apparatus according to the present invention;

[0028]FIG. 8 shows another optical coherent receiver employing the digital phase recovering device that incorporates frequency offset compensation apparatus according to the present invention;

[0029]FIG. 9 shows another optical coherent receiver employing the phase offset compensating apparatus according to the present invention; and

[0030]FIG. 10 shows an optical communication system employing the coherent receiver according to the present invention.

Problems solved by technology

However, insofar as optical coherent reception is concerned, due to restrictions of such factors as the technologies and standardization of optical devices, it is very difficult to implement a phase locked loop in the receiver to carry out precise control of the local oscillator laser.

Due to restrictions of such factors as the technologies and criteria of optical devices, it is very difficult to realize the receiver as shown in FIG. 1.

Consequently, when the frequency offset is greater than tens of MHz, the digital phase recover cannot operate normally.

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